The present invention relates to a method of manufacturing a printed circuit board having circuit patterns formed on one or both sides of an insulating substrate of the board and a shield layer overlaid on the circuit patterns.
As an example of a method of manufacturing a printed circuit board, there is known a method of manufacturing a printed circuit board having a shield layer formed on an overlaid insulating layer in order to shield circuit patterns formed on one or two sides of an insulating substrate of the board from electromagnetic noise coming from other circuit patterns also formed on the board or from external instruments. Such a conventional method is disclosed for example in Japanese Patent Publication No. 29276/1980.
As shown in FIG. 2, a printed circuit board manufactured by such a conventional method comprises an insulating layer 4 adhered onto a required part of a circuit pattern 2 formed on one side of an insulating substrate 1 by use of conductive material, a shield layer 5 adhered to a junction land 3 to maintain an electrical connection with a grounding circuit through the junction land 3, and a protecting film 6 formed to protect the shield layer 5.
Japanese Patent Publication No. 22885/1990 discloses another method of manufacturing a printed circuit board. As shown in FIG. 3, a printed circuit board manufactured by this method has a cross-mesh shield layer 10 formed in place of the shield layer 5 of prescribed thickness shown in FIG. 2.
When a cross-mesh shield layer 10 is formed according to the conventional method of manufacturing a printed circuit board, copper paste is applied by silk-screen printing. This method has a drawback, however, in that the outer periphery of the shield layer 10 or that of lands 7 and 8 are formed as a discontinuous portion, as shown in FIG. 3. As a result, the ability to shield against noise from electromagnetic waves is deteriorated in these discontinuous regions. Furthermore, when forming the shield layer 10, copper paste oozes from the outer periphery to the inside of the lands 7 and 8, and causes additional defects.